Tissue regeneration, inflammation and tumors induce the growth of new blood vessels from pre-existing ones. This process, angiogenesis, is a vital requirement for wound healing as the formation of new blood vessels allows a variety of mediators, nutrients, and oxygen to reach the healing tissue (Martin 1997, Singer & Clark 1999, Falanga 2006, Folkman 2006). Newly formed blood vessels differ in structure from pre-existing vasculature. Such differences have been extensively characterized by comparing tumor vasculature to normal vessels (Ruoslahti, 2002). Angiogenic vessels in non-malignant tissues and in pre-malignant lesions share markers with tumor vessels (Gerlag et al, 2001), but distinct markers also exist (Hoffman et al., 2003; Joyce et al., 2003).
Regarding tissue injuries, substantive basic science and clinical research have been conducted to evaluate the mechanisms of wound healing, the efficacy of various modalities for treatment of wounds, and the best methods for diagnosing wound infection. Tissue injuries caused by trauma, medical procedures, and inflammation are a major medical problem. Systemic medication is available for most major medical conditions, but therapeutic options in promoting tissue regeneration are largely limited to local intervention. As deep injuries and multiple sites of injury often limit the usefulness of local treatment, systemic approaches to tissue regeneration are valuable.
A major problem limiting tissue regeneration is scar formation. The response to tissue injury in adult mammals seems to be mainly focused on quick sealing on the injury. Fibroblast (astrocyte, smooth muscle cell) proliferation and enhanced extracellular matrix production are the main element of the scar formation, and the scar prevents tissue regeneration. In contrast, fetal tissues heal by a process that restores the original tissue architecture with no scarring. Transforming growth factor.beta. (TGF-.beta.) is a major factor responsible for impaired tissue regeneration, scar formation and fibrosis (Werner and Grose 2002; Brunner and Blakytny 2004; Leask and Abraham 2004).
A major hurdle to advances in treating cancer is the relative lack of agents that can selectively target the cancer while sparing normal tissue. For example, radiation therapy and surgery, which generally are localized treatments, can cause substantial damage to normal tissue in the treatment field, resulting in scarring and loss of normal tissue. Chemotherapy, in comparison, which generally is administered systemically, can cause substantial damage to organs such as the bone marrow, mucosae, skin and small intestine, which undergo rapid cell turnover and continuous cell division. As a result, undesirable side effects such as nausea, loss of hair and drop in blood cell count often occur when a cancer patient is treated intravenously with a chemotherapeutic drug. Such undesirable side effects can limit the amount of a drug that can be safely administered, thereby hampering survival rate and impacting the quality of patient life. For decades, researchers have examined avenues to increase targeted specificity of therapeutics against only the disease, thereby preserving normal cellular integrity.
One manner by which therapeutic specificity may be increased is by targeting diseases at the cellular level. More specifically, therapeutics may be enhanced by interacting directly with those components at the level of the cell surface or membrane. These components include, among others, laminin, collagen, fibronectin and other proteoglycans. Proteoglycans are proteins classified by a posttranslational attachment of polysaccharide glycosaminoglycan (GAG) moieties each comprised of repeating disaccharide units. One monosaccharide of the disaccharide repeat is an amino sugar with D-glucosamine or galactosamine, and the other unit is typically, but not always, a uronic acid residue of either D-glucuronic acid or iduronic acid. Both units are variably N- and O-sulfated, which adds to the heterogeneity of these complex macromolecules. They can be found associated with both the extracellular matrix and plasma membranes. The most common GAG structures are dermatan sulfate (DS), chondroitin sulfate (CS), heparan sulfate (HS), keratan sulfate (KS), hyaluronic acid (HA), and heparin; representative structures for each disaccharide are shown below.

These unbranched sulfated GAGs are defined by the repeating disaccharide units that comprise their chains, by their specific sites of sulfation, and by their susceptibility to bacterial enzymes known to cleave distinct GAG linkages. All have various degrees of sulfation which result in a high density of negative charge. Proteoglycans can be modified by more than one type of GAG and have a diversity of functions, including roles in cellular adhesion, differentiation, and growth. In addition, cell surface proteoglycans are known to act as cellular receptors for some bacteria and several animal viruses, including; foot-and-mouth disease type O virus, HSV types 1 and 2 and dengue virus. Accordingly, it would be advantageous from a therapeutic perspective to design agents which may be used at the cell surface level.
A major function of cell surface proteoglycans is in cell adhesion and migration, dynamic processes that are mediated through interactions between the proteoglycan GAG chains and extracellular matrix (ECM) components, such as laminin, collagen, and fibronectin. Proteoglycans also occur as integral components of basement membranes in most mammalian tissues. Interactions of these macromolecules with other ECM constituents contribute to the general architecture and permeability properties of the basement membrane, and thus these GAGs play a structural role. Proteoglycans and GAGs play a critical role in the pathophysiology of basement membrane-related diseases, including diabetes, atherosclerosis, and metastasis. In addition, cell-specific growth factors and enzymes are immobilized in the ECM and at the cell surface are bound to GAGs. As such, GAGs localize proteins and enzymes at their site of action to facilitate their physiological functions and in some cases prevent their proteolytic degradation. Proteoglycans and GAGs have been shown to regulate protein secretion and gene expression in certain tissues by mechanisms involving both membrane and nuclear events, including the binding of GAGs to transcription factors (Jackson, R. L. 1991). Limited information is available on the factors that regulate the expression of proteoglycans and their associated GAGs. There is a need in the art to develop cell-penetrating agents which bind to cell surface proteoglycans in order to have disease-specific efficacy.
US Patent Application Publication No. 20090036349 discloses a novel composition that selectively binds to regenerating tissue, wound sites and tumors in animals. In vivo screening of phage-displayed peptide libraries was used to probe vascular specialization. This screening method resulted in the identification of several peptides that selectively target phage to skin and tendon wounds. One peptide in particular was identified and contains the following sequence: CARSKNKDC (CAR) (SEQ ID NO:1). CAR displays homology to heparin-binding sites in various proteins, and binds to cell surface heparan sulfate and heparin. More specifically, CAR binds to glycosaminoglycan moieties in cell surface heparan sulfate proteoglycans (HSPGs) (Jarvinen and Ruoslahti 2007), and other cell-penetrating peptides have also mediated their entry into cells through binding to HSPGs (Poon and Gariépy 2007). HSPGs fine-tune mammalian physiology and orchestrate metabolism, transport, information transfer, support and regulation at the systemic level, as well as the cellular level (Bishop, Schuksz and Esko 2007). Overexpression of HSPG biosynthetic enzymes result in distinct heparan sulfate sulfation patterns (Pikas, Erikson and Kjellen 2000). The overexpression of HSPG biosynthetic enzymes have not been previously detected in a disease in which the co-administration of a cell penetrating peptide along with a bioactive agent which results in the disease-selective action of the co-administration of the peptide/agent combination.
There is a need for selectively targeting specific sites of action through co-administration of a targeting peptide with a bioactive agent in order to increase the efficacy of the combination therapy.